1. Field of the Invention
The present invention relates to a preliminary catalytic converter (“pre-converter”) device for cleaning exhaust gas, that contains hydrocarbons, which are emitted from an internal combustion engine. In particular, the pre-converter device has a perforated sleeve that is coated with a catalytic material to form an active surface. The area of the active surface increases as the distances from the pre-converter inlet increases. The pre-converter device is configured such that the active surface area on the pre-converter device increases as the temperature of the exhaust gases within the pre-converter device increases and the gas expands.
2. Description of Related Art
The typical operation of internal combustion engines creates exhaust gases. The pollutant content of these exhaust gases must meet certain legally prescribed requirements. The content is usually determined during a cycle of operations including a cold start and idling operations. A catalytic converter is often used to cleanse the exhaust gas. These requirements cannot be met unless the catalytic converter can become quickly operational (i.e., rapidly heated). Typically, a catalytic converter is arranged in the exhaust manifold directly following the cylinder. This arrangement is helpful during cold starting because the catalytic converter is rapidly heated. This location of the converter, however, impairs the functional performance of the exhaust system because of the amount of space occupied by the converter. The reduction in performance of the exhaust system has a direct impact on engine performance including a deterioration of the power, a reduction in the torque delivered, and an increase in fuel consumption. Furthermore, the close proximity of the converter to the engine cylinders can cause undesired reactions on the cylinder.
German Patent No. DE 10002024 C1 discloses catalytic device that is positioned between a first and a second section of the reactor. The catalytic device includes a boundary wall containing a catalytic material in the form of a foam or woven material that separates the two sections. Gases are directed from the first section into the second section through catalytic device. DE 100002024 discloses various configurations of the catalytic device including a conical tapered shape device having an enlarged end adjacent the first section and a reduced end adjacent the second section, a cylindrical shaped device having a plurality of channels extending along the axis of the device, and a cylindrical shaped device having a wavy exterior having portions with reduced diameter. These devices have been found to be inefficient and inadequate in treating the gas. In particular, these devices do not account for the expansion of the exhaust gas as it is heated while passing through the catalyst.
Others have tried to provide converters that become quickly operational during a cold start while not being placed in close proximity to the exhaust port. U.S. Pat. No. 5,012,642 to Laimböck discloses a converter having diffuser pipe connected thereto, which extends within the diffuser to a position adjacent the exhaust port. UK Patent Application No. 2,220,150 discloses tapering an upstream end of the converter to produce more rapid heating during cold starting.
Japanese Patent Nos. 5-86843 and 10-325315 disclose that it is known to provide a main catalytic converter, which is preceded by a preliminary catalytic converter. The provision of the pre-converter permits the main converter to be located a greater distance from the exhaust port. As such, the impact on engine performance is reduced. The pre-converter is used to clean exhaust gas and increase the temperature of the exhaust gases. The pre-converter ensures that the exhaust gas is at a proper temperature to activate the main converter and of a proper composition. Use of a pre-converter reduces the quantity of unburned hydrocarbons normally found in the exhaust gases emitted by an internal combustion engine. It is desirable to locate the pre-converter is disposed as close as possible to the cylinder of the internal combustion engine so that the high temperatures occurring adjacent to the cylinder will cause the pre-converter to be become quickly operational. Locating the pre-converter in too close a proximity to the cylinder will produce the above-described reduction in engine performance.
U.S. Pat. No. 5,014,510 to Laimböck discloses a pre-converter positioned in an exhaust system adjacent the exhaust port of the engine. The location of this pre-converter suffers from many of the above-described drawbacks including an adverse impact on engine performance. Furthermore, the pre-converter extends across the entire cross-section of the exhaust system, which adversely impacts the flow dynamics of the exhaust gases within the exhaust system and performance.
European Patent Application No. 411,561 discloses a pre-converter positioned in close proximity to the exhaust port of the engine. The location of this pre-converter adversely impacts engine performance. The pre-converter is positioned around the inner circumference of the exhaust system. As such, all of the exhaust gases from the cylinder do not flow through the pre-converter.